For the regeneration of particle filters in the exhaust gas of combustion engines fuel is injected into the exhaust gas duct of the combustion engine before an oxidization catalyzer and catalytically combusted in that oxidization catalyzer. Thereby the temperature of the exhaust gas is increased so far until the burn-off temperature of the particles that are accumulated in the downstream built-in particle filter is achieved. The particles are then combusted in an exothermal reaction.
For metering fuel into the exhaust gas duct first fuel is supplied to a metering valve over a security valve that is under pressure. Therefore the security valve is completely opened. The metering of the required fuel quantity takes place over the metering valve, which is controlled continuously or correspondingly cycled.
Due the high temperature in the exhaust gas duct the metering valve cannot be attached directly at the exhaust gas duct. Therefore an injection check valve is provided, over which the fuel is injected into the exhaust gas duct coming from the metering valve.
The calculation of the metering quantity takes place with the aid of a pressure measurement between the security valve and the metering valve. A second pressure measurement is provided between the metering valve and the injection valve and serves for the leakage detection in the metering device.
DE 10 2004 061 247 A1 describes a procedure for operating a combustion engine, in whose exhaust gas area an exhaust gas treatment device is arranged, at which a reagent is inserted into the exhaust gas area upstream before the exhaust gas treatment device, at which in the streaming direction of the reagent, which is set to a default reagent swelling pressure (pQRea), first a switchable reagent security valve (ReaCV), then a continuous reagent metering valve (ReaDV) and then a reagent injection check valve (ReaIV) are arranged, at which the reagent pressure (pRea) in the reagent path is detected, which lies between the reagent security valve (ReaCV) and the reagent metering valve (ReaDV), at which the reagent pressure (pRea) that has been detected in at least one default state of the reagent security valve (ReaCV) and/or the reagent metering valve (reaDV) is compared with a threshold value (pU, pabg, dpReaIV, dpReaCV, pQRea, dpRea/dt) and at which an error signal (F) is provided at a threshold exceeding.
DE 10 2004 061 247 A1 furthermore describes a device for operating a combustion engine. It is thereby provided that at least one control unit that is customized for implementing the procedure is provided.
Procedure and device enable the detection of a leakage in the reagent path as well as the checking of the function of the valves that are arranged in the reagent path.
The disadvantage of the familiar procedures and devices is that the metering accuracy of the fuel into the exhaust gas duct depends on tolerances of the injection check valve and is correspondingly limited.
It is the task of the invention to provide a procedure and a device, which improve the metering accuracy of the fuel metering into the exhaust gas duct.